Forward versus backward walking: Transfer of podokinetic adaptation

We asked whether podokinetic adaptation to walking on a circular treadmill transfers to different forms of locomotion. Subjects were blindfolded and a sked to walk straight across the floor, in the forward and backward directi ons, following podokinetic (PK) stimulation that consisted of 30 min of for ward walking-in-place on the perimeter of a disk rotating in the clockwise direction. During both forward and backward walking following forward-walki ng PK stimulation, subjects involuntarily walked along curved trajectories at angular velocities well above vestibular threshold, although they percei ved that they were walking along straight paths. The curved paths of forwar d and backward walking were indistinguishable from one another. Transfer of PK adaptations acquired during forward walking on the turntable to backwar d walking trials suggests that the PK system controls general locomotor tra jectory. Adaptation of the system thus influences forms of locomotion other than that used during acquisition of the adaptation. This transfer also su pports the concept that forward and backward walking are controlled by neur al networks that share common elements. An interesting feature of the trans fer of PK adaptation is that for both forward and backward walking, subject s turned in a counterclockwise direction. As such, the direction of relativ e rotation between the trunk and feet was maintained for both forward and b ackward walking. However, the relationship of the lower extremities to the center of rotation was not preserved. The left limb was the inner leg durin g PK stimulation and forward walking after adaptation, but the left leg was the outer leg during backward walking. These results suggest that PK adapt ation affects general locomotor trajectory via a remodeling of the rotation al relationship between the trunk and the feet.